The role of glucagon-like peptide-1 (GLP-1) has become a new scientific interest in the field of patho- physiology of type 1 diabetes mellitus (T1DM), but the results of the published studies were contradictory. The aim of our study was therefore to measure fasting and postprandial GLP-1 concentrations in T1DM patients and in healthy controls and to examine the difference in those concentrations between the two groups of subjects. The cross-sectional study included 30 C-peptide negative T1DM patients, median age 37 years (20–59), with disease duration 22 years (3–45), and 10 healthy controls, median age 30 years (27–47). Fasting and postprandial total and active GLP-1 concentrations were measured by ELISA (ALPCO, USA). The data were statistically analysed by SPSS, and significance level was accepted at P < 0.05. Both fasting total and active GLP-1 concentrations were significantly lower in T1DM patients (total 0.4pmol/L, 0–6.4 and active 0.2pmol/L, 0–1.9) compared with healthy controls (total 3.23pmol/L, 0.2–5.5 and active 0.8pmol/L, 0.2–3.6), P = 0.008 for total GLP-1 and P = 0.001 for active GLP-1. After adjustment for age, sex and body mass index, binary logistic regression showed that both fasting total and active GLP-1 remained significantly independently lower in T1DM patients (total GLP-1: OR 2.43, 95% CI 1.203– 4.909 and active GLP-1: OR 8.73, 95% CI 1.472– 51.787). T1DM patients had independently lower total and active GLP-1 fasting concentrations in comparison with healthy people, which supports the potential therapeutic role of incretin therapy, along with insulin therapy, in T1DM patients.